ObjectivesThis study compared the 3-year clinical performance of a low-shrinkage silorane-based composite material with that of a methacrylate-based composite material in the restoration of endodontically treated premolar teeth.Materials and methodsA total of 70 patients requiring a Class II composite-resin restoration of a premolar tooth following root-canal treatment participated in the study. Cavities were restored with either a silorane-based restorative (Filtek Silorane+Silorane System Adhesive) or a methacrylate-based restorative (Filtek Z250+Clearfil SE Bond) system applied according to the manufacturer's instructions. Restorations were evaluated by two blinded observers at five different time intervals (baseline; 6months; 1, 2, and 3years) according to modified USPHS criteria. Pearson's chi-square tests were used to examine differences in the clinical performance of the materials (retention, color match, marginal discoloration, secondary caries, anatomical form, marginal adaptation, and surface roughness), and Friedman and Wilcoxon tests were used to compare changes between baseline and each recall time, with a level of 0.05 considered statistically significant.ResultsAfter 3years, no statistically significant differences in clinical performance were observed between the two materials (p>0.05). Intra-system comparisons revealed a statistically significant deterioration in color match, marginal discoloration, anatomical form, marginal adaptation, and surface roughness scores after 3years for both systems. Although the difference was not significant at 3years of follow-up, the level of deterioration in marginal adaptation and surface roughness was greater for the Filtek Silorane restoration than for the Filtek Z250 restoration at the 1year follow-up (p>0.05).ConclusionRestorations of both materials were clinically acceptable after 3years. The Filtek Silorane system did not appear to offer any clinical advantages over the methacrylate-based system when used in the restoration of Class II cavities in endodontically treated premolars.Clinical relevanceThe restoration of endodontically treated premolars with minor or moderate loss of tooth structure can be directly performed either with silorane or methacrylate-based composite resins.